Cryosurgical system

ABSTRACT

A method of cooling selected surface areas of living tissues includes the steps of covering a resilient mass of porous material with a deformable liquid cryogen impervious membrane, conforming the membrane-covered mass to a configuration which corresponds to the size and shape of surface areas to be treated, pressing the preshaped membrane-covered mass into firm engagement with surface areas to be treated, and introducing a controlled supply of liquid cryogen into the mass. The step or pressing the membrane-covered mass into engagement with surface areas to be treated is performed with sufficient force to restrict or inhibit or cut off the normal flow of blood through the tissues thereby permitting the tissues to freeze more rapidly than would be possible if normal blood flow were maintained.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of application Ser. No. 423,013,filed Dec. 10, 1973 and now U.S. Pat. No. 4,022,215.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to cryogenic systems and moreparticularly to a cryogenic system for cooling selected surface areas ina safe, carefully controlled manner. While the highly versatile systemof the present invention has many non-medical uses in supercoolingselected surface areas, in cryo-adhesion, cryo-fragmentation,cryo-solidification of liquids, and the like, an important applicationis in the medical field of cryosurgery.

2. Prior Art.

The term "cryosurgery" relates broadly to a wide variety of surgicalprocedures wherein tissues are selectively destroyed by freezing withcryogenic materials.

While cold temperatures were reportedly used as early as the 1850's inthe treatment of such diseases as cancer, significant medical use ofcryogens did not occur until the 1890's. Processes for liquifying airwere developed as early as 1877, but the new product did not come intobroad use until the vacuum insulated cryogen storage vessel wasdeveloped nearly 15 years later.

Liquid air continued to be the principal liquified gas cryogen inmedical use until the 1940's when liquid nitrogen became available.Liquid nitrogen is preferable to liquid air and most other liquifiedgases for medical uses because it does not support combustion. Itcontinues to be the preferred cryogen for most medical purposes not onlybecause it is available very economically, but also due to its very highlatent heat of vaporization. Whereas, other available non-flammablecryogens such as CO₂, N₂ O and freon change phase at -90° centigrade orabove, liquid nitrogen changes phase at -196° centigrade. The resultingextraordinary latent heat of vaporization makes liquid nitrogen ofunique value in effecting a fast deep penetrating freeze in diseasedtissues.

Four cryogenic treatment techniques have been used with success:

(1) The swab method;

(2) The spray method;

(3) The open probe method; and

(4) The closed chamber probe method.

The swab method utilizes a swab such as a wooden stick with cottontightly twisted around one end to form an absorbent tip. The cottoncovered tip is dipped in a cryogen and then is placed on the tissue tobe treated. This direct application technique is not well adapted foruse with liquid nitrogen to treat large tissue areas or to effect deeppenetration freezing.

The spray method is another direct application technique where a cryogenmist is sprayed onto the tissue to be treated. This technique iscommonly used with liquid nitrogen to thinly freeze broad surface areas.It can also be used to obtain substantial depth of penetration withprolonged application. The spray method has several drawbacks includingdifficulty in achieving uniformity of penetration, and in controllingthe deflection of cryogen droplets from the primary target. Thesedrawbacks render the spray technique unsuitable for intra-cavity use andfor discrete site freezing-in-depth to controlled limits.

The open probe method utilizes a tubular probe having an open applicatorend which is pressed into surrounding engagement with a tissue surfaceto be treated. The tissue closes the applicator end and cooperates withthe tubular wall of the probe to define a chamber into which liquidcryogen is introduced for direct application to the tissue. Duringcryogen application, the tissue freezes firmly to the end of the probe.

The closed chamber probe method typically provides a probe structurehaving a relatively rigid tip cooled internally by cryogenic exposure.It differs from the swab, spray, and open probe methods, in that thecryogen itself is not brought into contact with the tissue to betreated. This better enables the probe to be used in intra-cavityapplications. Sufficient accuracy is attainable to enable discrete sitefreezing-in-depth. The closed chamber probe has even been used inmicro-surgery.

The freezing process is typically monitored by carefully observing itsprogress as indicated by changes of color and texture of tissues.Needle-like thermistor units implanted in the tissues to be frozen arealso used on occasion to provide a more exact indication of temperaturechanges as they occur.

The depth, extent and rate of freezing achieved with any cryoprobesystem depends on several factors, including the type of cryogen used,the area of contact between the cryoprobe and the target tissue, and thetime during which the tissue is exposed to cryogen cooling. Otherfactors which also come into play include the rate at which cryogen issupplied to the probe tip, and the efficiency of the probe intransferring heat out of the tissue and into the cryogen. Since thetarget tissues freeze rigidly to the probe tip during treatment and theprobe-to-tissue contact cannot be disrupted reliably without thawing,the freezing process is controllable chiefly by regulating the supply ofcryogen to the probe tip.

Early cryoprobes used in the 1900's included cylindrical and shpericalapplicators made of glass or brass which were filled with liquid androlled over the tissues to be treated. More sophisticated probes weredeveloped together with more precise instrumentation in the early 1960'sthrough the work of Dr. I. S Cooper. The Cooper system employed acannula about 2.2 mm. in diameter which ws vacuum insulated except forthe tip. The temperature of the tip was monitored by a thermocouplecontrol system which regulated the flow of liquid nitrogen to thecannula.

While various types of control systems are known for regulating the flowof cryogen to the tip of a probe, most of these known systems havevalves or other controls located at some distance from the site offreezing. Adjusting the flow of cryogen during surgery accordinglyrequires that apparatus outside the surgical field be manipulated. Thisis undesirable not only because it is often inefficient and clumsy, butalso because time delays are involved in effecting the adjustments andbefore uniform cryogen flow is re-established at the newly adjustedsetting.

Still another problem with known and proposed cryoprobes is that theytypically employ relatively rigid tips or applicator surfaces whichrarely conform with the tissue surfaces to be treated. The acceptedsolution has been to design a wide range of specialized probeconfigurations and to select the most appropriate available probe forsurgical use. Maintaining a large probe inventory is a costlyundertaking which is often frustrated by non-conformance of availableprobe shapes to the highly irregular and randomly variable shapes oftissue surfaces.

Most known probes cannot be reshaped due to the rigid nature of thematerials from which they are constructed. Most probes are also providedwith directed cryogen flow paths which become disrupted if the probe isdeformed, thereby rendering the probe unusable.

The use of a thin, softly compliant sleeve or membrane supported on ahard foamed plastic or metallic probe body is proposed in U.S. Pat. No.3,421,508, issued Jan. 14, 1969, to F. L. Nestrock. The applications towhich the Nestrock probe can be put are severely limited by therelatively rigid nature of the probe. It cannot be reshaped by handprior to use. The resilience of the probe is limited to the resilienceof the outer membrane or sleeve, and as such is not readily deformableto accommodate substantial tissue surface irregularities. The cryogenflow path through the probe tip requires a remotely controlled flowwhich is dependent upon the cryogen supply system design. The need for acarefully controlled cryogen flow through the probe severely limits theselection of probe sizes and shapes which can be used withoutredesigning the cryogen supply system. Moreover, the multi-partprecision machined nature of the probe assembly results in a very costlymedical apparatus.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing drawbacks of the prior artand provides an improved highly versatile cryogenic system having a widevariety of applications. When used in cryosurgery, the system permitsthe selective freezing of tissues in a safe, controlled manner. Itcombines the most desirable features of the spray and probe methods, andextends their utility.

An improved cryoprobe is provided having a tip which can be deformed toalmost any desired configuration prior to the probe's being filled witha cryogen, such as liquid nitrogen. The probe includes three majorparts: a tubular stem, a resilient porous mass of intertwined ormesh-like material, and a membrane.

The porous mass is formed into a ball and positioned adjacent one end ofthe tubular stem. the membrane is positioned over the mass and over theadjacent stem end region and compressively engages both the mass and thestem end region to secure the mass to the stem.

The tubular stem serves as a handle which can be grasped by a physicianto position the probe tip and press it in place against tissue to betreated. The stem also serves as a reservoir for cryogen. The stem istypically formed from a cold fracture resistent plastic tube. Aninsulative sheath of styrofoam or the like is wrapped around the tube toprotect the physician's hand from cold temperature cryogen within thetube.

The porous mass preferably comprises a good heat conductive metal suchas copper, aluminum or silver, but can comprise non-conductive materialssuch as nylon, dacron and polyethylene. The mass is highly porous toprovide a densely interconnected array of flow paths for transmittingliquid cryogen to the membrane, and for permitting the escape of cryogengas from the membrane surface back into the stem of the cryoprobe. Themass should also be deformable without destroying its porosity, andresilient after deformation. The preferred material for forming the massis an intertwined mesh of copper ribbon such as is used in a number ofcommercially available scouring pads.

The membrane comprises a thin pliable material which preferably has afinger-shaped configuration. A preferred material for forming themembrane is silicone rubber which resists deterioration with age and canbe autoclaved. An acceptable material is latex rubber of the typecommonly used in a surgeon's glove. The membrane must have sufficientstructural integrity to effectively isolate cryogen from the tissuesbeing treated, and yet it must be thin enough to permit efficient heattransfer. Both latex and silicone rubber are acceptable in that they donot become excessively brittle at subzero temperatures and can be reusedrepeatedly. They thaw and regain elasticity quickly after profoundfreezing and they are easily detached from frozen tissue. Moreover, theyare sufficiently transparent to permit visualization of the boilingaction of the cryogen in the copper mesh, thereby permitting visualmonitoring of the cryogen supply.

An insulation barrier of preselected shape can be interposed between thecopper mesh and the surrounding membrane to limit the size of the coppermesh applicator surface, and to provide an area which can safely beengaged by the physician's hand in exerting pressure on the probe tip.By this arrangement, normal tissues surrounding tissues to be treatedcan be protected from the freezing action of the cryogen. Any portion ofthe probe tip can be insulated, and the insulation can be positionedexternally as well as internally of the membrane. A flexible styrofoaminsulating material is preferred, but other types of insulation can beused.

The membrane can also be provided with a closed inflatable air-bag orcompartment. When inflated, the air-bag can serve the dual functions ofinsulating selected regions of the probe tip from tissues in thevicinity of the target tissues, and of assisting in thrusting theuninsulated tip portions into firm engagement with the target tissues.Such inflatable probes are advantageously used in difficult to exposeregions such as the throat and the colon. They can be inserted whiledeflated and then inflated to effect proper positioning.

Probe tips of a variety of sizes can easily be constructed by adding orsubtracting porous material. Probe tips of almost any desired shape canbe fashioned from the porous mass, thereby giving the probe greatversatility of use.

One or more semi-rigid preshaped rods or tubes extending from within thetubular stem into the porous mass can be used to help maintain thedesired configuration of the tip and to provide a means of pressing theprobe tip into engagement with tissues. These rods or tubes arepreferably, but not necessarily, formed from a heat conductive malleablematerial such as copper or aluminum. The rods or tubes are necessary insome applications where the target surface is the curved wall of achannel or cavity not offering wide areas of access. In suchapplications the probe tip requires auxiliary support to permit itsbeing pressed firmly against tissue to be treated. A tube used in thismanner, may also serve as a cryogen conduit to the probe tip.

In use the cryoprobe tip is preshaped to a desired configuration and isthen pressed into position against the tissues to be treated. Sufficientpressure is ordinarily used to inhibit warm blood flow within thetissues, whereby the tissues can be more quickly frozen. As the probetip is pressed in place, the resilience of the porous mass permits it toconform to tissue surface irregularities thereby obtaining an optimalconductive heat transfer juncture with the tissues.

Once the tip is pressed into place, cryogen is introduced into the stemof the probe and into the porous mass. The porous mass cools quickly andheat transfer from the tissues being treated begins promptly. Thefreezing cycle continues for several minutes whereafter the tissues areallowed to thaw. The freezing cycle is ordinarily repeated at least onceto assure that all living cells in the target area have been damaged.

The destruction of tissues by freezing has several advantages over otherapproaches. First, the cold temperatures tend to deaden local nerveendings with the result that the patient is subjected to less pain bothduring and after the treatment. Second, the freezing process can be usedto treat growths around large blood vessels with greater safety thanother methods. In such situations as where a tumor has developed aroundan artery in the neck, burning or cutting out the tumor may cause theartery to rupture. This is not as likely to happen with freezing, so therisk to the patient is less.

Third, in some instances, diseased bone tissues can be salvaged. Forexample, where a portion of a jawbone is diseased, it is customary tosaw out the diseased portion and either leave a defect, or substitute abone graft or a metal plate. With cryogenic freezing, the cells in thediseased area of the bone can be killed and the bone left structurallyintact, thereby eliminating the need for a bone graft or a metal plate.The dead bone will very gradually be replaced by new bone growth.

In accordance with another aspect of the present invention, two types ofcryogen supply systems are provided for feeding cryogen to the probe.One system provides a cryogen dispenser which is used to fill the stemof the cryoprobe where the probe will be used in a tip-down attitude.The other system is a continuous flow system for supplying cryogen tothe porous mass of a probe tip where the probe is used at any angle ofinclination from a tip-down attitude to a tip-up attitude.

The dispenser bottle supply system comprises an insulated cold-fractureresistent plastic bottle with a neck opening closed by a two-holestopper. A short vent tube extends through one hole of the stopper andinto the upper inner region of the bottle. A longer dispensing tubeextends through the other hole of the stopper and into the lower innerregion of the bottle.

The bottle is prepared for dispensing by filling it with liquid cryogen,and securing the stopper in place such that the dispensing tube extendsinto the liquid cryogen. With the vent tube open, the gas generated bythe bubbling, boiling cryogen escapes to the atmosphere. Dispensing isachieved simply by blocking the vent tube, whereupon gas pressure buildsup in the bottle and forces liquid cryogen out the dispensing tube.

One advantage of the cryogen dispenser bottle is its simple design andvery low cost. Another advantage is that it can be held in one hand andoperated simply by placing the index finger of the same hand over thevent tube. Before and after use, the dispenser bottle can be stored in aready location, typically on a surgical instrument table. Still anotheradvantage is the safety and accuracy with which cryogen dispensing canbe performed. The dispensing action ceases abrubtly once the vent tubeis open, enabling carefully controlled quantities of cryogen to bedispensed without danger of spillage.

The continuous feed supply system utilizes the same sort of cryoprobestructure described above. Dual flexible conduits communicate with theprobe stem. One of the conduits delivers cryogen to a position adjacentthe porous mass. The other conduit connects with a vacuum source forevacuating the probe stem. By controlling the vacuum evacuation of thestem, a continuous supply of cryogen can be drawn through the supplytube and discharged into the porous mass, thereby enabling the probe tobe used at any angle of inclination from tip-down to tip-up attitudes.

The dispenser bottle system can be converted to a continuous feed systemfor use with small sized probes. Dual conduits communicating with theprobe stem are provided with one extending into the cryogen supply ofthe dispenser bottle, and the other either open to the atmosphere, orconnected to a collector bottle which is open to the atmosphere. Whenthe dispenser bottle vent opening is closed, pressure build-up withinthe dispenser bottle forces cryogen into the probe. The membranecovering larger sized cryoprobes can inflate and/or rupture withexcessive nitrogen gas pressure in the initial phase of activation, ifdue care is not exercised in the use of this method.

The improved cryoprobes of the present invention add versatility toknown cryosurgical techniques since the probe tip can be formed toalmost any desired shape. The cryogen supply systems provide simple andinexpensive means for supplying cryogen in a safe, controlled manner tothe probe.

Multiple target areas and excessively large target areas can be treatedthrough the simultaneous use of multiple probes. While known cryoprobesupply systems are specially designed to accommodate a single probe of aspecific type, the supply systems of the present invention can be usedsimultaneously with multiple probes of different sizes andconfigurations to dispense cryogen from a single source.

As will be apparent from the foregoing, it is a general object of thepresent invention to provide a novel and improved cryogenic systemincluding cryogenic apparatus and techniques employing it.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of one probe embodiment of the presentinvention;

FIG. 2 is a perspective view of the probe of FIG. 1 when assembled;

FIG. 3 is a cross-sectional view of another probe embodiment;

FIG. 4 is a cross-sectional view of one embodiment of a cryogendispenser for supplying liquid cryogen to the probes of FIGS. 1-3;

FIG. 5 is a schematic perspective view of still another probe embodimentcoupled to a vacuum flow cryogenic supply system;

FIG. 6 is an enlarged cross-sectional view of a portion of thecollection bottle used in the system of FIG. 5, as seen from the planeindicated schematically by the line 6-6 in FIG. 5;

FIGS. 7-10 are perspective partial views of typical alternate probe tipconfigurations;

FIG. 11 is a schematic illustration of still another probe embodiment asemployed in the throat of a patient to freeze a tonsil; and

FIG. 12 is a cross-sectional view of the probe of FIG. 11 as seen fromthe plane indicated by the line 12-12 in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a cryoprobe constructed in accordance withthe present invention is shown generally at 10. The cryoprobe includes asupporting tubular stem 11, a flexible porous mass of intertwined ormesh-like material 12, and a thin pliable finger-shaped membrane 13. Thestem 11 has open end regions 14, 15.

In assembly, the porous material 12 is formed into a ball-shaped masspositioned adjacent the lower end region 14 of the stem 11. The membrane13 is drawn over the porous mass 12 and onto the stem end region 14. Themembrane 13 is resilient and compressively engages the porous mass 12and the stem end region 14. An insulating sheath 16 is wrapped aroundthe stem 11 and adhered in place to provide a handle structure that canbe safely held by a physician when liquid cryogen is present inside thestem.

The stem 11 serves at least four functions. First it provides arelatively rigid support for the cryoprobe tip and serves as a handle toposition and guide the tip. Second, it provides a conduit for channelingliquid cryogen from the upper end region where it is introduced into thestem, to the lower end region where it is delivered to the porous mass12. Third, it serves as a cryogen reservoir and is typically filled withcryogen to about one-half of its capacity when the cryoprobe is in use.Finally, it serves as an exhaust conduit for cryogen gas.

The stem 11 is preferably formed from a relatively rigid tube of plasticmaterial such as polyethylene or polypropylene. It can be formed ofother materials such as paper, wood, photographic film or othermaterials which do not tend to crack or become dangerously brittleduring the severe temperature change which takes place when the stem isfilled with liquid nitrogen.

The insulative sheath 16 preferably comprises a thin sheet of styrofoamwhich is wrapped around the stem 11 and is adhered in place. Otherconventional insulative materials such as glass wool, multiple layers ofpaper or plastic film, etc. can be used. The insulative sheath 16 canalso be formed integrally with the stem 11. The sheath 16 should providesufficient insulation to protect the hands of a physician from the lowtemperature cryogen within the stem 11, but should not be so bulky as toadd unnecessarily to the size or weight of the cryoprobe 10.

The porous mass 12 serves at least three functions. First, it provides adensely interconnected array of flow paths for the delivery of liquidcryogen to regions near the membrane 13 and for simultaneous escape ofcryogen gas formed by evaporation. Second, it provides a readilydeformable supporting tip structure which can easily be shaped to adesired configuration prior to use, thereby giving the cryoprobe greatversatility of shape. Third, it provides a resilient tip structurewhich, even after it has been deformed to a desired shape, is stillsufficiently resilient to conform to tissue irregularities.

The porous mass 12 serves still another function where the material fromwhich it is formed has a high coefficient of heat transfer, as with suchmaterials as copper, aluminum and silver. The good heat conductivity ofsuch materials enables the mass to assist in maintaining a uniformtemperature gradient at all points along the surface of the membrane 13.

The material from which the mass 12 is formed presents a highly porousarray of random flow paths to the cryogen. It is the multi-directionalinterconnected nature of these flow paths which permits the mass to besubstantially deformed and preshaped without losing its ability tosupply cryogen to the membrane surface. The mass 12 must also be formedfrom materials which are not so pointed or so rigid as will puncture themembrane 13.

Non-conductive materials such as wool, cotton, nylon, polyester,polyurethane, etc. can be used to form the mass 12, particularly wherethe stem 11 is held vertically with the mass 12 at the lower end so themass is effectively filled with cryogen due to gravitational forces. Insuch instances as will later be described where the probe tip must beheld above the stem 11 during use and cryogen is continuosly sprayedinto the mass 12, the mass 12 is preferably formed from highlyconductive materials such as copper or aluminum to assure that the coldtemperatures are transmitted to the membrane surface. Mixtures ofmetallic and non-metallic porous materials may be utilized as well.

The membrane 13 serves at least three functions. First, it acts as ameans for securing the porous mass 12 to the stem 11. The membrane 13compressively engages the stem end region 14 and holds the mass 12 inplace adjacent the stem 11. Second, the membrane isolates the cryogenfrom tissues being treated while not appreciably impairing the transferof heat from the tissues to the cryogen. Third, the pliability of themembrane 13 adds to the resilience of the cryoprobe tip therebyfacilitating the ability of the tip to conform to tissue irregularities.Where the membrane 13 is formed of substantially transparent material,it serves the added function of permitting visual monitoring of thecryogen boiling which takes place within the mass 12.

The preferred material from which the membrane 13 is formed is purelatex rubber of the type used in a surgeon's glove. A surgeon's glovefinger has been found to form a very acceptable membrane. Other latexrubber finger-shaped membranes are commercially available in the form offinger cots. While materials other than latex rubber can be used, vinylmaterials and the like have been found to provide a less efficient heattransfer medium, and to exhibit excessive cold fragility and inferiorresistance to puncture.

The thickness of the membrane 13 has been found to be of significantimportance. Membranes of about one-half mil (i.e., about 0.013millimeter) work significantly better than membranes of one milthickness in that they permit a significantly faster, more efficientheat transfer.

It is also important that the membrane not become brittle at lowtemperatures and that it be reusable repeatedly. Latex rubber has theseproperties and is also desirable from the viewpoint of its ability toregain elasticity quickly after profound freezing, whereby it is easilyand safely detached from frozen tissue.

It is frequently desirable to insulate certain regions of the cryoprobetip (1) to confine extraction of heat to selected tissue areas; (2) toprevent accidental damage to nearby tissues which may unintentionallycome into engagement with the cold probe tip; and (3) to provide aninsulated backing on the probe which can be safely touched by aphysician in pressing the probe tip into firm engagement with tissuesbeing treated. Any portion of the probe tip can be insulated, and theinsulation can be positioned internally or externally of the membrane13. A flexible styrofoam insulating material is preferred because a thinsheet can be used effectively without adding significantly to the sizeof the cryoprobe tip.

Referring to FIG. 2, a sheet of styrofoam insulation 20 is showninterposed between portions of the porous mass 12 and the membrane 13.The styrofoam sheet 20 encircles most of the perimeter of the porousmass 12, leaving only an applicator region 12a exposed for use.

A significant feature of probes constructed in accordance with thepresent invention is that the size of the probe tip can be increased ordecreased simply by adding more porous material to the mass 12, orremoving some porous material from the mass 12. The volume of the massdoes not appreciably affect the random flow characteristics of thecryogen. Larger masses do consume more cryogen in the initial process ofdecreasing their temperature, but once the mass is cooled, probeoperation tends to be the same whether the mass is relatively large orsmall, providing cryogen supply is maintained. Larger probes will, ofcourse, consume more cryogen than do smaller probes.

Referring to FIG. 3, an alternate probe embodiment is shown generally at10' as including a stem 11', a porous mass 12' and a membrane 13'. Theprobes 10, 10' differ principally in that (1) the porous mass 12' is oflarger size than the porous mass 12; (2) the porous mass 12' is ofcurved configuration as opposed to the relatively straight configurationof the mass 12; and, (3) a metallic rod 17' extends through the stem 11'and into the porous mass 12' to assist in maintaining the mass 12' in acurved configuration.

The metallic rod 17' does not interfere with the flow of cryogen throughthe mass 12'. It helps maintain the curved configuration of the mass 12'and if extended out the upper end region 15' of the stem 11' can providea means for manipulating the probe tip and for applying pressure to thetip.

Referring to FIGS. 5 and 7-10, still other alternate probe tipembodiments are shown at 110, 210, 310, 410, 510 as including stems 111,211, 311, 411, 511 and porous masses 112, 212, 312, 412, 512 surroundedby membranes 113, 213, 313, 413, 513. Insulation sheets are providedbetween these membranes and portions of the porous masses to exposeselected applicator areas of the porous masses.

In use, the cryoprobe tip is first shaped to the general configurationof the surface of the tissue to be treated. The tip is then pressed intoengagement with the tissue. A sufficient amount of pressure is, in mostinstances, used to shut off the normal blood flow to the tissue beingtreated, and to drive out the blood that is initially in the tissue.Once this is done, cryogen is introduced into the cryoprobe and theprocess of freezing the tissue begins. Cryogen is introduced into thestem until the stem is about half full. The freezing process progressestypically for about 2 to 5 minutes, whereafter the tissues are permittedto thaw for about 2 to 5 minutes. Ordinarily at least a second freezingcycle is used to assure that no uninjured cells remain in the targetarea. While cell death is not assured by freezing, it becomes highlyprobable if cell temperature drops below about -40° C.

During the freezing process, the cryogen bubbles and boils audiblywithin the stem of the cryoprobe. As the supply of cryogen is depleted,the bubbling action in the area of the copper mesh can be observed tocease.

After the treated tissues have been frozen at least twice, they areordinarily left alone for about 5-10 days. During this time, the tissuesordinarily go through a process of discoloring to a blue or black color.The tissues ordinarily swell taking on fluid, but eventually theswelling regresses and the tissues wither away. In some instances, thedead tissue is surgically removed several days after it has been frozen.Biopsies are then taken of the surrounding living tissue to assure thatall the diseased tissue has been killed. If additional living diseasedtissue is found, it is frozen and removed.

Referring to FIG. 4, a cryogen dispenser for introducing liquid cryogeninto the stem 11 of a cryoprobe is shown generally at 30. The dispensercomprises a cold-fracture resistant plastic bottle 31 having a neckopening 32 closed by a two-hole stopper 33. A short gas vent tube 34extends through one hole of the stopper 33 and communicates the upperinterior region of the bottle with the atmosphere. A longer curved orbent tube 35 extends through the other hole of the stopper 33. The upperend region of the tube 35 is formed into a nozzle shaped configuration36. The lower end region 37 of the tube 35 extends into the lowerinterior region of the bottle 31. An insulative jacket 38 is providedaround the bottle 31. The jacket preferably comprises glass fiber woolwith an insulating tape cover.

In use, the stopper 33 is removed from the neck opening 32 and thebottle 31 is about half filled with liquid cryogen. The stopper 33 isthen replaced. The short vent tube 34 permits cryogen gas to excape fromthe upper interior region of the bottle. The longer dispensing tube 37extends into the liquid cryogen supply.

The cryogen is dispensed simply by closing off the vent tube 34.Typically, a physician holds the dispenser 30 in his hand and places hisindex finger over the upper end of the vent tube 34 to initiate cryogendispensing. With the tube 34 closed, the gas released from the bubblingcryogen into the upper inner region of the bottle 31 creates a positivepressure which forces liquid cryogen up through the dispensing tube 35and out the nozzle 36. This dispensing action can be stopped almostinstantaneously by opening the vent tube 34.

It is not always possible to use the cryoprobe 10 in an erect, tip-downattitude. In some surgical applications, the probe must be usedsubstantially horizontally and even vertically in a tip-up attitude.Where this is the case, a continuous flow cryogen supply system is usedto deliver cryogen to the porous mass 12 of the cryoprobe tip.

Referring to FIG. 5, the cryoprobe 110 can be used at substantially anyangle of inclination from tip-down to tip-up attitudes. As has beenexplained, the cryoprobe 110 is structurally identical to the probe 10in its inclusion of a stem 111, a porous mass 112, and a membrane 113.

A supply tube 121 and an exhaust tube 122 communicate with the probe110. The supply tube 121 has one end region 123 extending into a supplyof liquid cryogen stored in a conventional thermo-insulated cryogenreservoir bottle 124. The other end region 125 of the supply tube 121extends through an aperture 120 in the exhaust tube 122 and into theporous mass 122 to a position near the inner surface of the membrane113. The supply tube 125 may also function as the equivalent of metallicrod 17' shown in FIG. 3.

The exhaust tube 122 has one end region 132 which extends over the endof the stem 111 in sealing engagement therewith. The exhaust tube 122 islarger in diameter than the supply tube 121 to prevent clogging by iceformations, and compises a tube which is flexible but which is alsoresistant to collapse when vacuum evacuated. The other end region 133 ofthe exhaust tube 122 extends through a stopper 134 and into a liquidtrap or collection bottle 135. A vacuum source conduit 136 also extendsthrough the stopper 134 into the collection bottle 135. A pop-uppressure valve 137 is provided in the stopper 134, as shown in FIG. 6,to prevent pressure buildup which could otherwise occur when thecollection bottle 135 is not being vacuum evacuated.

In operation, the vacuum conduit 136 is connected to a vacuum source(not shown). As a vacuum develops within the trap 135, the tube 122, thestem 111, and the tube 121, liquid cryogen is drawn through the tube 121and discharged into the porous mass 112. Cryogen continues to flow intothe mass 112 as long as the vacuum is maintained. Any liquid cryogenwhich enters the vacuum tube 122 will drip into the trap 135 where itwill evaporate.

Since the supply system of FIG. 5 is a closed continuous supply system,the probe 110 can be inverted or used at any required angle without thedanger of spilling cryogen.

The dispenser bottle 30 can be converted to a continuous feed dispensersystem for use with relatively small probes. The conversion isaccomplished simply by connecting the dispensing tube 35 to a closedprobe supply tube such as the tube 121 on the probe 110. Dispensing isthen effected simply by closing the vent tube 34, whereby pressurebuildup in the bottle 30 will feed cryogen to the probe. This type ofdispensing system can be used without assistance of a vacuum evacuationapparatus, or can be used to augment cryogen supply in vacuum evacuatedsystems.

Referring to FIGS. 11 and 12, still another probe embodiment 610 isshown which has advantageous application in hard-to-reach areas such asthe throat and colon. In the manner of the above-described probes, theprobe 610 includes a stem 611, a porous mass 612 and a membrane 613. Theprincipal difference between the probe 610 and previously describedprobes is that the membrane 613 is specially formed to include a closedinflatable compartment or air-bag 620. A tube 621 communicates with thecompartment 620 for admitting and discharging air.

As shown in FIG. 11, the probe 610 is well adapted for use in freezingtonsil tissues. It is positioned in the throat of a patient with theair-bag 620 deflated. When in position, the air-bag 620 is inflated bycompressed air supplied through the tube 621. The inflation of theair-bag 620 insulates the porous mass 612 from tissues around the tonsiltissues being treated, and helps to press the porous mass 612 into firmmating contact with the tonsil tissues.

After the tonsil tissue has been frozen, the air-bag 620 is deflated toreduce the size of the probe tip, whereafter the probe 610 is withdrawnfrom the patient's throat.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand numerous changes in the details of construction and the combinationand arrangement of parts may be resorted to without departing from thespirit and scope of the invention as hereinafter claimed.

What is claimed is:
 1. A method of cooling selected surface areas ofliving tissues comprising the steps of:(a) covering a resilient mass ofporous material with a deformable liquid cryogen impervious membranecapable of confining liquid cryogen within said mass; (b) conforming themembrane covered mass to a configuration which corresponds to the sizeand shape of the surface areas to be treated; (c) pressing the preshapedmembrane covered mass into firm engagement with the surface areas to betreated; (d) introducing a controlled supply of liquid cryogen into saidmass whereby the porous mass ducts the liquid cryogen along a denselyinterconnected array of flowpaths into contact with said membrane andheat is transferred from the surface areas to be treated through saidmembrane to said liquid cryogen; and, (e) the step of pressing themembrane covered mass into engagement with the surface areas to betreated being performed with sufficient force to cut off the normal flowof blood through said tissues thereby permitting said tissues to freezefar more rapidly than would be possible if normal blood flow weremaintained during the initial stages of freezing.
 2. The method of claim1 wherein the pressure applied to the surface areas to be treated issufficient to drive out the blood that is initially in the tissue.
 3. Amethod of cooling selected surface areas of living tissues comprisingthe steps of:(a) covering a resilient mass of porous material with adeformable liquid cryogen impervious membrane capable of confiningliquid cryogen within said mass; (b) conforming the membrane coveredmass to a configuration which corresponds to the size and shape of thesurface areas to be treated; (c) pressing the preshaped membrane coveredmass into firm engagement with the surface areas to be treated; (d)introducing a controlled supply of liquid cryogen into said mass wherebythe porous mass ducts the liquid cryogen along a densely interconnectedarray of flowpaths into contact with said membrane and heat istransferred from the surface areas to be treated through said membraneto said liquid cryogen; and, (e) the step of pressing the membranecovered mass into engagement with the surface areas to be treated beingperformed with sufficient force to restrict the normal flow of bloodthrough said tissues thereby permitting said tissues to freeze far morerapidly than would be possible if normal blood flow were maintainedduring the initial stages of freezing.
 4. The method of claim 3 whereinthe pressure applied to the surface areas to be treated is sufficient todrive out the blood that is initially in the tissue.
 5. A method ofcooling selected surface areas of living tissues comprising the stepsof:(a) covering a resilient mass of porous material with a deformableliquid cryogen impervious membrane capable of confining liquid cryogenwithin said mass; (b) conforming the membrane covered mass to aconfiguration which corresponds to the size and shape of the surfaceareas to be treated; (c) pressing the preshaped membrane covered massinto firm engagement with the surface areas to be treated; (d)introducing a controlled supply of liquid cryogen into said mass wherebythe porous mass ducts the liquid cryogen along a densely interconnectedarray of flowpaths into contact with said membrane and heat istransferred from the surface areas to be treated through said membraneto said liquid cryogen; and, (e) the step of pressing the membranecovered mass into engagement with the surface areas to be treated beingperformed with sufficient force to inhibit warm blood flow within thetissues thereby permitting said tissues to freeze more rapidly thanwould be possible if normal blood flow were maintained during theinitial stages of freezing.
 6. The method of claim 5 wherein thepressure applied to the surface areas to be treated is sufficient todrive out the blood that is initially in the tissue.